1. Field of the Invention
This invention relates to disk drives, and particularly disk drives of the multi-actuator variety. Still more particularly, the invention concerns the generation of timing information for writing permanent embedded servo information in a multi-actuator disk drive.
2. Description of the Prior Art
During disk drive manufacture, the writing of embedded servo sectors requires precise reference timing in order to adequately phase align the servo patterns when moving from one track to the next. This timing function has traditionally been performed by an external clock head that flies at a fixed location over a surface of one of the disk platters (e.g., at its outer diameter) during the servo write process. The clock head either writes and then reads its own timing information, or reads previously written timing information.
A disadvantage of external clock head servo writing is that it is not possible to servo write a sealed disk file insofar as the clock head needs to physically access the disk surface. This requirement makes conventional external clock head servo writing relatively complicated. The clock head must first be loaded onto the disk file that is to be servo written. This entails introducing the clock head through an opening that is formed in the disk file base casting. Following servo writing, the clock head must be unloaded and the opening in the disk file base casting must be closed to seal the disk file.
Because of their repeated loading and unloading on successive disk files, clock heads have a limited life and require regular replacement. If they become contaminated or damaged prior to replacement, they can destroy a good disk file or propagate contamination from one disk file to another.
An additional disadvantage of external clock head servo writing is that disk real estate which could be otherwise utilized for data storage is typically used to hold the timing information.
One prior art alternative to external clock head servo writing is to use self-propagating clock tracks in a scheme known as NCH (No Clock Head) servo writing. According to this technology, a product head used for servo writing is first positioned at a known reference location, such as the disk outer diameter. There, it writes a track containing clock information. The product head then steps progressively across the disk surface and, in iterative fashion, writes servo information as well as new clock information while using clock information written in a previous iteration for timing. A disadvantage of self-propagating clock track servo writing is that the process requires an additional revolution of the disk on many tracks to measure the time intervals under most combinations of head geometry and slider skew.
Multi-actuator disk drives have been developed in which the drive actuators are assigned to carry out data storage operations on mutually-exclusive disk areas. An example of such a drive is shown in commonly assigned U.S. Pat. No. 5,761,007. This drive comprises a pair of actuators that are mounted for independent rotation about a common pivotal axis. The principal advantage of multi-actuator drives of this type is that more than one actuator is used to access disk real estate normally covered by a single actuator, which increases access times and data transfer rates. As far as known, however, conventional multi-actuator disk drives of the foregoing type, including the dual-actuator drive of U.S. Pat. No. 5,761,007, use conventional servo writing techniques, and thus suffer from the disadvantages referred to above.
It is submitted that improvements in servo write timing generation are needed in order to expeditiously perform servo writing, particularly in a multi-actuator disk drive production environment. What is required is a servo write method that obviates the need for an external clock head or NCH servo write techniques, is relatively simple in design, and which maximizes the amount of disk real estate available for data storage.
The foregoing problems are solved and an advance in the art is obtained by a method in which a multi-actuator disk file having at least two actuators respectively mounting plural product heads is written with embedded servo information using the product heads themselves. A first servo write operation is initially performed that includes operating a product head of a first one of the actuators as a first clock head to generate first clock reference information. Using the first clock reference information, the product heads of a second one of the actuators are operated as servo write heads to perform servo writing of disk areas associated with the second actuator. Following the first servo write operation, disk areas associated with the first actuator are servo written using a second servo write operation. This operation includes operating a product head of the second actuator as a second clock head to generate second clock reference information. Using the second clock reference information, the product heads of the first actuator are operated as servo write heads to perform servo writing of the disk areas associated with the second actuator.
In preferred embodiments of the invention, the clock reference information generating steps include positioning the acting clock heads at disk data area edges. This positioning may be accomplished by biasing the actuators carrying the clock heads against actuator crash stops or other positioning members. Alternatively, the clock heads can be positioned by servoing. The timing information read by the clock heads may represent clock tracks, timing triggers or other indicia. Such information may either be pre-written on the disk or written and then read back by the clock heads themselves.
If desired, the second clock head can write the second timing information using the first timing information. In that case, the first clock head will read the first timing information while the second clock head writes the second timing information in a predetermined tangential orientation relative to the first timing information. This will provide timing alignment between the actuators.
In cases where the disk drive includes more than two actuators, the first servo write operation will include operating a product head of a first actuator as a first clock head while the product heads of one or more of the plural remaining actuators perform servo writing. The second servo write operation will then include operating one of the product heads already used for servo writing as a second clock head while the product heads of the first actuator, and any remaining actuators, perform servo writing.
In another aspect of the invention, a disk drive is provided having multiple actuators respectively mounting plural product heads that read and write information on associated disk areas. At least two of the disk areas may have first and second timing information respectively recorded thereon and all of the disk areas have servo sectors recorded thereon according to the above-described servo writing method.
In a further aspect of the invention, a system is provided for servo writing a multiple actuator disk file. Part of the servo write system includes components of the disk file, including the disk assembly, a first actuator having product heads that access a first portion of the disk assembly, a second actuator having product heads that access a second portion of the disk assembly, and a disk drive controller. The remainder of the servo write system includes a programmable data processing host that is external to the disk file but communicates therewith via a control cable, and a servo write control program that may run as an external software program on the host processor, as an internal firmware program on the drive controller, or a combination of both. The servo write control program includes program instructions for performing servo writing in the manner described above.